If Approvers don't receive approval notifications, the reason might be that this feature has been switched off in My Profile. Users can check their profile settings themselves.
This is how you switch on notifications:
Go to your avatar in the top right-hand corner and click on My profile:
Here, you'll find the section about email notifications. You can toggle the status for each notification type by clicking on
. The button turns blue and the respective notification is switched on. Save your changes.